The invention relates to a picture display device having a vacuum envelope which is provided with a transparent face plate with a display screen having a pattern of picture elements (pixels) luminescing in different colours, and with a rear plate. The display device comprises a plurality of juxtaposed electron propagation means extending substantially parallel to the face plate, and an addressing system, arranged between the electron propagation means and the face plate, to selectively address desired pixels on the screen.
The display device described above is of the flat-panel type, as disclosed in EP-A-464 937. Display devices of the flat-panel type are devices having a transparent face plate and, arranged at a small distance therefrom, a rear plate, with the inner surface of the face plate being provided with a (hexagonal) pattern of phosphor dots. If (video information-controlled) electrons impinge upon the luminescent screen, a visual image is formed which is visible via the front side of the face plate. The face plate may be flat or, if desired, curved (for example, spherical or cylindrical).
The display device described in EP-A-464 937 comprises a plurality of juxtaposed sources for emitting electrons, local electron-propagation means cooperating with the sources and each having walls of high-ohmic, substantially electrically insulating material having a secondary emission coefficient suitable for propagating emitted electrons, and an addressing system with electrodes (selection electrodes) which can be driven row by row for withdrawing electrons from the propagation means at predetermined extraction locations facing the luminescent screen, further means being provided for directing extracted electrons towards pixels of the luminescent screen for producing a picture composed of pixels.
The operation of the picture display device disclosed in EP-A-464 937 is based on the recognition that electron propagation is possible when electrons impinge on a wall of a high-ohmic, substantially electrically insulating material (for example, glass or synthetic material) if an electric field of sufficient power is generated over a given length of the wall (by applying a potential difference across the ends of the wall). The impinging electrons then generate secondary electrons by wall interaction, which electrons are attracted to a further wall section and in their turn generate secondary electrons again by wall interaction, and so forth.
Starting from the above-mentioned principle, a fiat-panel picture display device can be realised by providing each one of a plurality of juxtaposed "compartments", which constitute propagation ducts, with a column of extraction apertures at a side which is to face a display screen. It will then be practical to arrange the extraction apertures along "horizontal" lines extending transversely to the ducts. By adding selection electrodes arranged in rows to the arrangement of apertures, an addressing means is provided with which electrons can be selectively withdrawn from the "compartments" and directed (and accelerated) towards the screen for producing a picture composed of pixels by activating the pixels.
The addressing system can be of the single-stage type, or of the multi-stage type. EP-A-464 937 particularly describes a multi-stage addressing system. A multi-stage addressing system using a number of preselection extraction locations, which number is reduced with respect to the number of pixels, and associated therewith a number of (fine-) selection apertures, which corresponds to the number of pixels, provides advantages with respect to the extraction efficiency and/or with respect to the required number of connections/drivers. For controlling the preselection locations a pattern of preselection electrodes is used, and for controlling the (fine) selection apertures a pattern of fine-selection electrodes is used.
In the traditional display tubes the pitch of the shadow mask is typically 2 to 3 times smaller than the spot size. The resolution, i.e. definition of the display is then determined by the spot size, while the precise details of the colour dots within a shadow mask pitch are less important. In displays having discretely addressed colour dots the pitch of the colour dot structure is of the same order as the resolution of the display. Since a too high resolution of the display is expensive, when using a given signal, it is important to choose the resolution of the display in the vicinity of the desired resolution. Hence, the details of colour dot structure are more important than in the tradition display tube.